ec2

# AWS EC2

Amazon Elastic Compute Cloud (EC2) provides resizable compute capacity in the cloud.

**Advanced patterns** (Auto Scaling, Spot Fleets, Session Manager, Instance Connect, IMDS, Placement Groups, scheduled scaling): see [instance-management.md](instance-management.md).

## Table of Contents

- [Core Concepts](#core-concepts)
- [Common Patterns](#common-patterns)
- [CLI Reference](#cli-reference)
- [Best Practices](#best-practices)
- [Troubleshooting](#troubleshooting)
- [References](#references)

## Core Concepts

### Instance Types

| Category | Example | Use Case |
|----------|---------|----------|
| General Purpose | t3, m6i, t4g (Graviton) | Web servers, dev environments |
| Compute Optimized | c6i, c7g (Graviton) | Batch processing, gaming |
| Memory Optimized | r6i, r7g (Graviton) | Databases, caching |
| Storage Optimized | i3, d3 | Data warehousing |
| Accelerated | p4d, g5 | ML, graphics |

Graviton (ARM) instances (t4g, m7g, c7g, r7g) are ~20% cheaper than x86 equivalents for the same performance — worth considering for new workloads.

### Purchasing Options

| Option | Description |
|--------|-------------|
| On-Demand | Pay by the hour/second |
| Reserved | 1-3 year commitment, up to 72% discount |
| Spot | Unused capacity, up to 90% discount — can be interrupted with 2-minute notice |
| Savings Plans | Flexible commitment-based discount |

### AMI (Amazon Machine Image)

Template containing OS, software, and configuration for launching instances. Use SSM Parameter Store to look up the latest official AMIs rather than hardcoding IDs:

```bash
# Latest Amazon Linux 2 AMI
aws ssm get-parameter \
  --name /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2 \
  --query 'Parameter.Value' --output text

# Latest Amazon Linux 2023
aws ssm get-parameter \
  --name /aws/service/ami-amazon-linux-latest/al2023-ami-kernel-default-x86_64 \
  --query 'Parameter.Value' --output text

# Latest Ubuntu 22.04
aws ssm get-parameter \
  --name /aws/service/canonical/ubuntu/server/22.04/stable/current/amd64/hvm/ebs-gp2/ami-id \
  --query 'Parameter.Value' --output text
```

### Security Groups

Virtual firewalls controlling inbound and outbound traffic. Changes take effect immediately — no restart required.

## Common Patterns

### Launch an Instance

```bash
# Create key pair
aws ec2 create-key-pair \
  --key-name my-key \
  --query 'KeyMaterial' \
  --output text > my-key.pem
chmod 400 my-key.pem

# Create security group
aws ec2 create-security-group \
  --group-name web-server-sg \
  --description "Web server security group" \
  --vpc-id vpc-12345678

# Allow SSH and HTTP
aws ec2 authorize-security-group-ingress \
  --group-id sg-12345678 \
  --protocol tcp \
  --port 22 \
  --cidr 10.0.0.0/8

aws ec2 authorize-security-group-ingress \
  --group-id sg-12345678 \
  --protocol tcp \
  --port 80 \
  --cidr 0.0.0.0/0

# Launch instance
aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type t3.micro \
  --key-name my-key \
  --security-group-ids sg-12345678 \
  --subnet-id subnet-12345678 \
  --associate-public-ip-address \
  --tag-specifications 'ResourceType=instance,Tags=[{Key=Name,Value=web-server}]'

# Wait until running, then get IP
aws ec2 wait instance-running --instance-ids i-1234567890abcdef0
aws ec2 describe-instances \
  --instance-ids i-1234567890abcdef0 \
  --query 'Reservations[].Instances[].PublicIpAddress' --output text
```

**boto3:**

```python
import boto3

ec2 = boto3.resource('ec2')

instances = ec2.create_instances(
    ImageId='ami-0123456789abcdef0',
    InstanceType='t3.micro',
    KeyName='my-key',
    SecurityGroupIds=['sg-12345678'],
    SubnetId='subnet-12345678',
    MinCount=1,
    MaxCount=1,
    TagSpecifications=[{
        'ResourceType': 'instance',
        'Tags': [{'Key': 'Name', 'Value': 'web-server'}]
    }]
)

instance = instances[0]
instance.wait_until_running()
instance.reload()
print(f"Instance ID: {instance.id}")
print(f"Public IP: {instance.public_ip_address}")
```

### User Data Script

> **OS package manager note:**
> - **Amazon Linux 2**: use `amazon-linux-extras install nginx1 -y` — `yum install nginx` fails because nginx is not in the default AL2 repos
> - **Amazon Linux 2023**: use `dnf install -y nginx`
> - **Ubuntu**: use `apt-get install -y nginx`
> - **Amazon Linux 2 / RHEL**: `httpd` (Apache) is always available via `yum install -y httpd`

```bash
# Amazon Linux 2 — nginx via amazon-linux-extras
aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type t3.micro \
  --key-name my-key \
  --security-group-ids sg-12345678 \
  --subnet-id subnet-12345678 \
  --user-data '#!/bin/bash
amazon-linux-extras install nginx1 -y
systemctl start nginx
systemctl enable nginx
'

# Amazon Linux 2 — httpd (Apache, simpler alternative)
# --user-data '#!/bin/bash
# yum install -y httpd
# systemctl start httpd
# systemctl enable httpd
# echo "<h1>Hello from $(hostname -f)</h1>" > /var/www/html/index.html
# '
```

### Attach IAM Role

```bash
# Create instance profile
aws iam create-instance-profile \
  --instance-profile-name web-server-profile

aws iam add-role-to-instance-profile \
  --instance-profile-name web-server-profile \
  --role-name web-server-role

# Launch with profile
aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type t3.micro \
  --iam-instance-profile Name=web-server-profile \
  ...
```

### Create AMI from Instance

```bash
aws ec2 create-image \
  --instance-id i-1234567890abcdef0 \
  --name "my-custom-ami-$(date +%Y%m%d)" \
  --description "Custom AMI with web server" \
  --no-reboot
```

### Auto Scaling Group with Spot (Modern Approach)

The recommended way to use Spot Instances at scale is via Auto Scaling Groups with a mixed-instances policy — not the legacy `request-spot-instances` API. This supports instance diversification to minimize interruptions.

See [instance-management.md](instance-management.md) for the full setup. Quick example:

```bash